Separation and recovery of nickel and cobalt in ammoniacal systems

ABSTRACT

A process for the separation and recovery of nickel from an ammoniacal ammonium carbonate liquor containing nickel II ions and cobalt III ions by liquid-liquid extraction where ammoniacal ammonium carbonate solutions are the only aqueous phases involved in the process. The process includes the successive steps of: (a) oxidizing the majority of any cobalt II ammines in the ammoniacal liquid to cobalt III; (b) extracting nickel from the ammoniacal liquor with an organic reagent, which reagent may also contain a suitable modifying reagent, to form a nickel loaded organic phase and an ammoniacal ammonium carbonate phase containing cobalt; (c) stripping the nickel loaded organic phase characterized by contacting the organic phase with an ammoniacal ammonium carbonate solution to form a nickel loaded aqueous strip liquor.

The invention relates to a novel process for the separation and recoveryof nickel and cobalt. More specifically, it relates to the separationand recovery of nickel and cobalt values when present in aqueousammoniacal solution by solvent extraction and the recovery of theisolated nickel by aqueous ammonium carbonate stripping of thenickel-organic reagent complex.

Nickel and cobalt are valuable metals and their recovery from orescontaining these metals is the basis of widespread Industrial Processesof considerable importance. A common process for the recovery of nickeland cobalt from ores and concentrates is to use a reduction roastfollowed by an ammonia-ammonium carbonate leach process.

In such processes it is desirable to produce a basic nickel carbonate toallow for further processing. In order to produce a basic nickelcarbonate of suitable purity, it is necessary to first remove theassociated dissolved cobalt.

This is normally achieved by injection of a suitable sulphiding agent,for example, gaseous hydrogen sulphide or ammonium hydrosulphidesolution. This procedure results in some dissolved cobalt remaining insolution as well as the removal of some dissolved nickel, both of whichare undesirable.

In addition, the mixed nickel-cobalt sulphide formed, and other metalimpurities that are concurrently precipitated, have to be subjected to acomplex series of digestion, separation and recovery processes beforemetallic cobalt and metallic nickel, or suitable salts thereof, can beobtained.

The sulphiding process also introduces sulphur anions into theessentially cobalt-free nickel-rich process stream. The sulphur anionsare difficult to remove and contaminate the basic nickel carbonate whenit is precipitated. The presence of sulphur compounds in the basicnickel carbonate requires high calcination temperatures to produce asuitable low sulphur content nickel oxide product.

Liquid-liquid extraction processes are now well established inprocessing a wide range of metallic and non-metallic compounds. Theapplication of such a process to the present problem avoids the use of asulphiding compound, but it is often difficult to achieve the desiredresult.

In particular, nickel-cobalt separation by liquid-liquid extraction isrelatively difficult but can be effected under certain conditions, forexample, a suitable extraction can be achieved by contacting the organicreagent tri-iso-octylamine with a strongly acidic chloride solution ofnickel and cobalt in oxidation state II. Another example of theextraction is the application of di-2-ethylhexyl phosphoric acid orsimilar reagents, such as bis-(2,4,4-trimethylpentyl) phosphonic acidand 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester to acidicsulphate solutions containing nickel and cobalt in oxidation state II.

Further examples of the extraction step involve the application of oximetype reagents such as 2-hydroxy-5-t-nonyl acetophenone oxime and2-hydroxy-5-dodecyl benzophenoneoxime to ammoniacal ammonium sulphate orcarbonate solutions of nickel and cobalt, the latter in oxidation stateIII. An additional example of another type of reagent is the contactingof substituted beta-diketone reagents with ammoniacal ammonium carbonateor sulphate solutions of nickel and cobalt in oxidation state III.

During liquid-liquid extraction of nickel and cobalt using organicsolvents the aqueous phase that separates from the organic phase isusually termed the raffinate and contains the majority of the cobalt,while the organic phase contains the majority of the nickel. In order torecover the nickel, the nickel-rich organic phase is reacted (stripped)with a suitable aqueous acid, for example sulphuric acid, to return thenickel to an aqueous phase, the resulting aqueous solutions are fed toconventional metal winning circuits, e.g. electrowinning, to recovernickel and the cobalt.

Acid stripping of the nickel-containing organic layer should be avoidedif a basic nickel carbonate product is required. Prior to the presentinvention, a suitable non-acidic stripping medium capable of strippingnickel from commonly used organic reagents, such as 2-hydroxy-5-t-nonylacetophenoneoxime, 2-hydroxy-5-nonyl salicylaldoxime and alkyl, aryl,halide substituted beta-diketone type reagents has not been developed.

The process of the present invention helps to alleviate theabove-mentioned disadvantages of the prior art. It is an object of thepresent invention to provide a suitable stripping agent for the organiclayer that is non-acidic, eliminates contamination of the nickel bysulphur anions, and Can be readily incorporated into an ammoniacalprocess stream containing nickel and cobalt.

Accordingly, the present invention resides in a process for theseparation and recovery of nickel from an ammoniacal ammonium carbonateliquor containing nickel II ions and cobalt III ions by liquid-liquidextraction including the successive steps of:

(a) oxidising the majority of any cobalt II ammines in the ammoniacalliquor to cobalt III;

(b) extracting nickel from the ammoniacal liquor with an organic reagentto form a nickel loaded organic phase and an ammoniacal ammoniumcarbonate phase containing cobalt; and

(c) stripping the nickel loaded organic phase; characterised in that thenickel loaded organic phase is stripped by contacting the organic phasewith an ammoniacal ammonium carbonate solution to form a nickel loadedaqueous strip liquor and in that ammoniacal ammonium carbonate solutionsare the only aqueous phases involved in the process.

This process may be applicable to the separation of a wide range ofmetallic or non-metallic compounds. The process is particularly useful,however, for the separation of nickel and cobalt. More specifically, theprocess of this invention is particularly useful for separating nickelin oxidation state II and cobalt in oxidation state III. Otherseparations to which the present process may be applied include theseparation of copper and cobalt or of nickel and copper. However, forconvenience of description and understanding, the following descriptionwill concentrate on the separation of nickel and cobalt.

The ammoniacal ammonium carbonate liquor containing the metal and cobaltmay be heated prior to the oxidising step so as to precipitate unwantedelements and to reduce the ammonium content. It is preferred that theammoniacal ammonium carbonate liquor be heated to a temperature of about100° C. at atmospheric pressure and the ammonium content reduced tobetween 22 to 32 gl⁻¹. It is most preferred that the ammonia content isreduced to 25gl⁻¹ and the carbon dioxide content is 18gl⁻¹.

The process of the present invention involves a novel stripping agent tostrip a nickel-loaded organic phase, obtained after a liquid-liquidextraction of the nickel and cobalt. The process is particularlyapplicable to liquid-liquid extraction processes where aqueousammoniacal ammonium carbonate solutions have been used to dissolve themetals out of the ores, while the preferred type of organic reagentsused include acetophenoneoximes, salicylaldoximes, and beta-diketones.The organic reagents together with suitable modifiers, if required, forexample isotridecanol, may be dissolved in hydrocarbon solvents ofeither an aromatic or aliphatic nature. Other organic reagents may beused which preferentially extract nickel from aqueous solutionscontaining both nickel and cobalt but those named are currentlycommerically available and have been found particularly effective.

A particularly preferred organic solution may comprise about 32.5% v/v2-hydroxy-5-nonylaceto-phenoneoxime, 18.4% v/v iso-tridecylalcohol with49.1% v/v hydrocarbon solvent of less then 25% aromatic content. Thepreference for these quantities are based upon the specific ratiosbetween the oxime solution and the specific alcohol

The process is preferably applied to solutions in which theconcentration of nickel is within the range of 8-10 gl⁻¹. A nickelconcentration of about 9 gl⁻¹ appears to give optimum results, howeveradjustments to the circuit flow rates will compensate for both higherand lower nickel concentrations. The concentration of cobalt may varywidely in the solutions requiring separation without appearing to affectthe efficiency of the separation.

The majority of the nickel will usually separate into the organic phasein which it will form a neutral nickel II organo-metallic complex withan organic/nickel molar ratio of 2. Cobalt III does not react with theorganic reagents but cobalt II forms similar organo-metallic complexesto nickel II.

It is preferred that the ammoniacal liquor is contacted with the liquidorganic solution containing the organic reagent for a period of between30 seconds to 60 minutes. Most preferably the content time is for aperiod of about 3 minutes.

The majority of the cobalt, which is present as cobalt III, remains inthe aqueous phase (raffinate). The cobalt in the raffinate may berecovered in any appropriate manner, for example by sulphiding.

Any nickel remaining in the raffinate can be recovered by appropriateprocedures if such recovery is considered economically viable or isotherwise necessary.

The organic phase from the extraction step is then treated in order torecover the nickel. In order to achieve a desirable medium for theproduction of a basic nickel carbonate, the process of this inventioninvolves contacting the nickel-containing organic phase with an aqueousammoniacal ammonium solution, so as to recover the nickel by bringing itback into an aqueous solution.

The ammoniacal ammonium carbonate solution may contain excess ammoniaand is preferably stronger than the ammoniacal ammonium carbonatesolution used to leach the ore. The concentration of the solution usedto recover the nickel from the loaded organic phase is preferably in theranges of NH₃ :210-300 gl⁻¹, CO₂ :150-250 gl⁻¹. The solution strengthcurrently most preferred is NH₃ :270 gl⁻¹, CO₂ :230 gl⁻¹.

The contact between the loaded organic phase the ammoniacal ammoniumcarbonate solution may be carried out at any appropriate temperature andpressure. Preferably this step is conducted at atmospheric pressure andat a temperature in the range of 20° C. to 50° C.

It is preferred that the nickel loaded organic phase is contacted withthe ammoniacal ammonium carbonate solution for a period of between 30seconds to 60 minutes. Most preferably the content time is for a periodof about 3 minutes.

Both the separation and stripping process can be carried out by aconventional batch extraction technique or by a continuous mixer settlertechnique. The latter technique is generally preferred as it recyclesthe stripped organic phase in a continuous manner, thus allowing the onevolume of organic reagent to be repeatedly used for nickel recovery.

When the process of the invention is applied to the operation of acontinuous counter current mixer-settler apparatus, the organic/aqueousratio in the stripping cells is preferably in the range of 6.0-10.0:1.This contrasts with the preferred organic/aqueous range in theextraction cells (where comparable organic agents may be used) of1.0-1.2:1.

It is preferred that the nickel loaded organic phase is stripped in astripping cell at a temperature of about 40° C.

The nickel that separates into the aqueous phase can be recovered as anickel carbonate by any conventional manner. For example, basic nickelcarbonate can readily be recovered by distillation. Nickel can also berecovered effectively from aqueous ammonium carbonate solution byhydrogen reduction under pressure. The recovery technique preferablyallows for the NH₃ and CO₂ components of the strip liquor to be recycledto the nickel loaded organic stripping stage.

The process of the present invention is illustrated with reference tothe following examples. It is to be understood that these examples aregiven by way of illustration only and are not to be construed aslimiting the scope of the invention as broadly described.

In all of the following examples 1 to 4, the liquors tested wereobtained from currently operating process stream and had the followinginitial approximate compositions:

    ______________________________________                                        Nickel           10.0        gl.sup.-1                                        Cobalt           0.46        gl.sup.-1                                        NH.sub.3         85          gl.sup.-1                                        CO.sub.2         62          gl.sup.-1                                        ______________________________________                                    

Prior to liquid-liquid extraction, this liquor was treated to lower thetotal ammonium content to a suitable strength of approximately 30 gl⁻¹.

EXAMPLE NO. 1

The organic extractant system consisted of 25 volumes of a(2-hydroxy-5-t-nonyl acetophenoneoxime) reagent dissolved in 75 volumesof kerosene of approximately 17% aromatic content. Test work was carriedout in the temperature range of 23° C. to 43° C. The mixer settlers usedwere sealed units to prevent loss of NH₃ and CO₂ to the atmosphere.

The batch extraction tests were conducted in the approximate ratio rangeof organic phase to aqueous phase of 10:1 to 1:10 in seven ratioincrements. For the continuous mixer/settler tests the organic toaqueous ratio of 1.64 was used.

Typical results for the batchwise loading tests are given in Table No. 1and the continuous mixer/settler test results are given in Table No. 2.

                  TABLE NO. 1                                                     ______________________________________                                        Feed liquor composition: Ni 14.4 gl.sup.-1, Co 0.48 gl.sup.-1                 (Approx.)        AQUEOUS     ORGANIC                                          ORGANIC/AQUEOUS  PHASE       PHASE                                            PHASE RATIO      Ni     Co       Ni   Co                                      ______________________________________                                        10:1             0.010  0.48     1.26 0.001                                   5:1              0.003  0.48     2.70 0.001                                   2:1              0.003  0.48     6.20 0.001                                   1:1              0.010  0.48     12.8 0.001                                   1:2              4.3    0.48     17.6 0.001                                   1:5              5.9    0.48     17.6 0.001                                    1:10            12.1   0.48     17.8 0.001                                   ______________________________________                                         All results in gl.sup.-1.                                                

                  TABLE NO. 2                                                     ______________________________________                                        Feed liquor composition: Ni 12.5 gl.sup.-1, Co 0.64 gl.sup.-1                                                   NICKEL                                                            (Raffinate) LOADED                                      EXT CELL 1                                                                              EXT CELL 2  EXT CELL 3  ORGANIC                                     ______________________________________                                        490 PPm Ni                                                                              5 PPm Ni    0.7 ppm Ni  8.48 gl.sup.-1                              ______________________________________                                    

The batch stripping tests were conducted in the range of organic toaqueous of approximately 10:1 to 1:10 in seven ratio increments. Thestripping solution was an ammoniacal ammonium carbonate solution.Typical results for the batch stripping tests are given in Table No. 3.

For the continuous mixer settler stripping test, the O/A ratio of 1.66was used and the results are given in Table No. 4.

                  TABLE NO. 3                                                     ______________________________________                                        Loaded organic phase: 18.0 gl.sup.-1 Ni                                                         Ni gl.sup.-1                                                ORGANIC/AQUEOUS   AQUEOUS      ORGANIC                                        APPROX. PHASE RATIO                                                                             PHASE        PHASE                                          ______________________________________                                        10:1              23.2         15.4                                           5:1               16.0         14.0                                           2:1               13.4         11.4                                           1:1               7.7          8.6                                            1:2               6.2          5.2                                            1:5               2.6          4.4                                             1:10             1.4          4.2                                            ______________________________________                                    

                  TABLE NO. 4                                                     ______________________________________                                        Loaded organic phase: 8.16 gl.sup.-1 Nickel                                   (All results gl.sup.-1 Ni)                                                    STRIP   STRIP     STRIP     STRIP   STRIPPED                                  CELL 1  CELL 2    CELL 3    CELL 4  ORGANIC                                   ______________________________________                                        (Loaded Strip Liquor)                                                         12.3    6.4       3.5       1.6     1.42                                      ______________________________________                                    

The data in Tables 1, 2, 3 and 4 clearly demonstrate the selectivity ofextraction and the efficiency of the discovered stripping media. Theresultant raffinate rich in cobaltic cobalt and loaded strip liquor richin nickel are suitable for downstream treatment to recover high puritycobalt and nickel materials respectively.

EXAMPLE NO. 2

The organic extraction system in this case consisted of 25 volumes of a2-hydroxyl-5-nonyl-salicylaldoxime reagent dissolved in 75 volumes ofkerosene of approximately 17% aromatic content. Apparatus and conditionsemployed were similar to those described above in Example No. 1. Typicalresults for the batchwise extraction tests are given in Table No. 5 andthe continuous mixer settler extraction test results are given in TableNo. 6.

                  TABLE NO. 5                                                     ______________________________________                                        Feed liquor composition: Ni 13.0 gl.sup.-1, Co 0-.42 gl.sup.-1                                 AQUEOUS     ORGANIC                                          (Approx.)        PHASE       PHASE                                            ORGANIC/AQUEOUS  Ni     Co       Ni   Co                                      PHASE RATIO      gl.sup.-1                                                                            gl.sup.-1                                                                              gl.sup.-1                                                                          gl.sup.-1                               ______________________________________                                        10:1             0.004  0.42     1.3  0.001                                   5:1              0.016  0.42     2.5  0.001                                   2:1              0.008  0.42     6.08 0.001                                   1:1              0.071  0.42     11.36                                                                              0.001                                   1:2              6.04   0.42     11.92                                                                              0.001                                   1:5              10.28  0.42     12.18                                                                              0.001                                    1:10            11.52  0.42     12.18                                                                              0.001                                   ______________________________________                                    

                  TABLE NO. 6                                                     ______________________________________                                        Feed liquor composition: Ni 12.36 gl.sup.-1, Co 0.62 gl.sup.-1                                                  NICKEL                                                            (Raffinate) LOADED                                      EXT CELL 1                                                                              EXT CELL 2  EXT CELL 3  ORGANIC                                     ______________________________________                                        195 ppm Ni                                                                              1.5 ppm Ni  1.0 ppm Ni  10.76 gl.sup.-1 Ni                          ______________________________________                                    

The batch stripping tests were conducted in approximate ratios rangingfrom 10:1 to 1:10 organic to aqueous in seven ratio increments. Thestripping solution was an ammoniacal ammonium carbonate solution. Theresults from the continuous mixer settler stripping test at an organicto aqueous ratio of 1.6 are given in Table No. 8.

                  TABLE NO. 7                                                     ______________________________________                                        Loaded organic phase: 12.4 gl.sup.-1 Ni                                                         Ni gl.sup.-1                                                ORGANIC/AQUEOUS   AQUEOUS      ORGANIC                                        APPROX. PHASE RATIO                                                                             PHASE        PHASE                                          ______________________________________                                        10:1              18.6         11.0                                           5:1               16.1         9.2                                            2:1               10.0         7.4                                            1:1               7.0          5.8                                            1:2               3.6          5.0                                            1:5               1.4          4.4                                             1:10             0.66         4.2                                            ______________________________________                                    

                  TABLE NO. 8                                                     ______________________________________                                        Loaded organic phase: 11.1 gl.sup.-1 Ni                                       (All results gl.sup.-1 Ni)                                                    STRIP   STRIP     STRIP     STRIP   STRIPPED                                  CELL 1  CELL 2    CELL 3    CELL 4  ORGANIC                                   ______________________________________                                        (Loaded Strip Liquor)                                                         14.1    6.7       3.2       1.7     2.72                                      ______________________________________                                    

The data in Tables 5, 6, 7 and 8 clearly demonstrate the selectivity ofextraction and the efficiency of the discovered stripping media. Theresultant raffinate rich in cobaltic cobalt and the loaded strip liquorrich in nickel are suitable for downstream treatment to recover highpurity cobalt and nickel materials respectively.

EXAMPLE NO. 3

The organic extraction system in this case consisted of 25 volumes of analkyl, aryl substituted beta-diketone reagent, dissolved in 75 volumesof kerosene with greater than 50% aromatic content. Apparatus andconditions employed were similar to those reported above in ExampleNo. 1. Typical examples for the batchwise extraction tests are given inTable No. 9 and the continuous mixer settler test results are given inTable No. 10.

                  TABLE NO. 9                                                     ______________________________________                                        Feed liquor composition:                                                      Nickel 12.9 gl.sup.-1, Cobalt 0.56 gl.sup.-1                                                   AQUEOUS     ORGANIC                                          (Approx.)        PHASE       PHASE                                            ORGANIC/AQUEOUS  Ni     Co       Ni   Co                                      PHASE RATIO      gl.sup.-1                                                                            gl.sup.-1                                                                              gl.sup.-1                                                                          gl.sup.-1                               ______________________________________                                        10:1             0.44   0.56     1.16 0.001                                   5:1              0.64   0.56     2.34 0.001                                   2:1              2.0    0.56     5.48 0.001                                   1:1              5.2    0.56     7.48 0.001                                   1:2              8.6    0.56     8.08 0.001                                   1:5              11.2   0.56     8.98 0.001                                    1:10            11.8   0.56     9.0  0.001                                   ______________________________________                                    

                  TABLE NO. 10                                                    ______________________________________                                        Feed liquor composition: Ni 12.36 gl.sup.-1, Co 0.57 gl.sup.-1                                                     NICKEL                                   EXT     EXT      EXT       (Raffinate)                                                                             LOADED                                   CELL 1  CELL 2   CELL 3    EXT CELL 4                                                                              ORGANIC                                  ______________________________________                                        5.64    1.46     0.27      0.069     6.34                                     ______________________________________                                    

The batch striping tests were conducted in approximate ratios rangingfrom 10:1 to 1:10 organic to aqueous in seven ratio increments. Thestripping solution was an ammoniacal ammonium carbonate solution.Typical results for the batch stripping tests are given in Table No. 11.

The results from the continuous mixer settler test at an organic toaqueous ratio of 4.9 are given in Table No. 12.

                  TABLE NO. 11                                                    ______________________________________                                        Loaded organic phase: 9.5 gl.sup.-1 Ni                                                          Ni gl.sup.-1                                                ORGANIC/AQUEOUS   AQUEOUS      ORGANIC                                        APPROX PHASE RATIO                                                                              PHASE        PHASE                                          ______________________________________                                        10:1              28.3         6.0                                            5:1               26.6         2.7                                            2:1               14.6         0.14                                           1:1               8.0          0.05                                           1:2               4.0          0.01                                           1:5               1.8          0.01                                            1:10             0.9          0.01                                           ______________________________________                                    

                  TABLE NO. 12                                                    ______________________________________                                        Loaded organic phase                                                                                            STRIPPED                                    STRIP CELL 1                                                                            STRIP CELL 2                                                                              STRIP CELL 3                                                                              ORGANIC                                     ______________________________________                                        (Loaded Strip Liquor)                                                         28.2 gl.sup.-1                                                                          2.2 gl.sup.-1                                                                             0.036 gl.sup.-1                                                                           2 ppm Ni                                    ______________________________________                                    

It will be noticed from these last two tables that the discoveredstripping liquor is extremely effective in recovering the nickel fromthe loaded organic phase.

The separation and recovery of nickel and cobalt in oxidation state IIIin completely ammoniacal systems is not restricted to ammoniacalammonium carbonate leachates of reduced laterities. Otherammonia-ammonium salt solutions in which cobalt is in oxidation stateIII can be successfully treated by the present invention. Aeration oroxidation of the ammonia-ammonium salt solution by other oxidants is apreferred method of bringing the dissolved cobalt into oxidation stateIII. For example, as will be shown by the following example, the methodis applicable to solutions resulting from the oxidation under Pressureof nickel cobalt sulphides producing nickel ammines and cobaltic (CoIII) ammines in ammoniacal solutions.

EXAMPLE NO. 4

The solution of nickel and cobalt was prepared by autoclaving a plantproduced nickel cobalt sulphide solid sample slurried at 15% solids W/Vin ammonium carbonate solutions (NH₃ 160, CO₂ 100 gl⁻¹) at 70° C. forthree hours at oxygen pressure 45 psig. The resultant solution has thefollowing composition.

    ______________________________________                                        Ni              32.4        gl.sup.-1                                         Co              14.0        gl.sup.-1                                         NH.sub.3        80          gl.sup.-1                                         CO.sub.2        64          gl.sup.-1                                         ______________________________________                                    

The organic extractant system used in this case in a bench shake-outtest was a 2-hydroxyl-5-nonyl acetophenoneoxime reagent (47% V/V) inkerosene. The apparatus and conditions used in the bench shake-out testswere similar to those reported above for Example No. 1. The results forthe batchwise tests are given in Table No. 13.

                  TABLE NO. 13                                                    ______________________________________                                        (Approx.)        AQUEOUS     ORGANIC                                          ORGANIC/AQUEOUS  PHASE       PHASE                                            PHASE RATIO      Ni     Co       Ni   Co                                      ______________________________________                                        10:1             0.012  14.0     3.2  0.001                                   5:1              0.056  14.0     7.2  0.001                                   2:1              5.9    14.0     13.2 0.001                                   1:1              18.0   14.0     14.0 0.001                                   1:2              24.6   14.0     14.0 0.001                                   1:5              28.2   14.0     14.0 0.001                                    1:10            30.6   14.0     14.0 0.001                                   ______________________________________                                         All results in gl.sup.-1.                                                

EXAMPLE NO. 5

A counter current liquid ion exchange circuit consisting of threeextraction cells, three stripping cells and one loaded organic wash cellis fed with an ammonium carbonate solution (25 gl⁻¹ NH₃, 14 gl⁻¹ CO₂)with 9 gl⁻¹ Ni and variable cobalt, 0.1 to 1.0 gl⁻¹ together with traceamounts of iron, manganese, copper and zinc.

The organic extractant used is a 42.5% V/V solution of an alkyl, aryl,beta-diketone dissolved in the high aromatic content solvent PegasolR150 sold by Mobil.

In the extraction stages the organic to aqueous ratio was 1 0:1.

The aqueous raffinate (cobalt III rich solutions) analysed 0.34 gl⁻¹cobalt, 0.005 gl⁻¹ nickel, averaged over a 24 hour continuous period.

The strip liquor feed solution Contained 240 gl⁻¹ NH₃ and 215 gl⁻¹ CO₂and contacted the nickel loaded organic reagent exiting extractant cellNo. 1 in an organic to aqueous ratio of 7.5:1. The ratio of the organicto aqueous phases in the mixer box was maintained at 1:1 or thereaboutsas necessary, by the use of aqueous recycle from the settler back to themixer in each individual cell.

The loaded strip solution analysed 68.6 gl⁻¹ nickel and 0.013 gl⁻¹cobalt averaged over a 24 hour period.

The stripped organic solution after exiting the final strip cell (S3)and before entering the final extraction cell (E3) analysed 0.10 gl⁻¹nickel and 0.006 gl⁻¹ cobalt.

The system was operated continuously for 96 hours at 30-40° C. with thestripped organic recycled from the stripping to the extraction cells viaa small volume intermediate vessel. The results reported above weretypical of those achieved during the operating

An alternative organic extractant for use in the above process is a27.5% V/V solution of a modified hydroxy oxime reagent. An alternativehigh azomatic content solvent is Solvesso 150 sold by Exxon. The organicto aqueous ratio in the extraction stages may be increased to 1.2:1 andthe continuity of the phases may be either aqueous continuous or organiccontinuous depending on which system produces the least organic reagententrainment losses.

The aforementioned description outlines the process as performed in alaboratory environment. The adaptation of this process into a pilotplant is outlined in the following description by reference to FIG. Iand the following specific example. It should be understood that thedrawinq and specific example are only illustrative and not intended tobe limitinq to the scope of the invention.

While the Pilot Plant was designed to process forty five (45) liters perminute of plant liquor it must be emphasized that by extrapolating theresults found for the Pilot Plant one skilled in the art can design acommercial Plant for processing large volumes of solution.

The operations performed in the Pilot Plant can be itemised as follows:

1. Solution Preparation

2. Solvent Extraction

3. Meta1 Stripping

4. Loaded Strip Liquor purification

5. Steam Stripping

6. Nickel Recovery

7. Cobalt Recovery.

SOLUTION PREPARATION

Ores containing cobalt and nickel values are prepared by forming anappropriate slurry. This preparation includes reducing the metal ores insize by crushing and grinding and chemically reducing by subjecting theores to suitable reductants while also heating.

The resultant slurry (21) is passed through aeration tanks (D) oxidisingthe majority of any cobalt II to cobalt III. The slurry is thensubjected to washing and thickening in tanks 1a to 7a. Tailings (23) areremoved after washing through tailings still (M) wherein steam (2) isadded and vapours (22) are condensed in Gas Cooler condenser (H). Anynon condensed vapours are passed to absorber (N) for dissolution inplant liquor and the resultant liquid recycled back to wash thickener7(a).

The Plant Product Liquor solution stream (1) of normal composition (9gl⁻¹ Ni, 0.4 gl⁻¹ Co, 85 gl⁻¹ NH₃ and 60 gl⁻¹ CO₂) is pumped through aheat exchanger (A) to a multiple tray distillation column (B). Steamfrom a 10 psi line (2) is injected into the bottom of the Still therebystripping some ammonia and carbon dioxide from the Plant Product Liquor.The amount of steam applied is carefully controlled to produce a liquorcontaining approximately 25 gl⁻¹ ammonia (NH₃) 18 gl⁻¹ carbon dioxideCO₂ with essentially the same concentration of nickel and cobalt as theincoming Product Liquor. This quantity of steam is of the order of 0.12kg steam per liter of Product Liquor feed. This liquor exiting thedistillation column is termed special product liquor and is identifiedas stream (3) and has the following approximate composition.

                  TABLE NO. 14                                                    ______________________________________                                        Nickel     7.3 g/l    Ammonia      28 g/l                                     Cobalt     0.35 g/l   Carbon Dioxide                                                                             18 g/l                                     Iron       1 ppm      Zinc         7 ppm                                      Manganese  1 ppm      Copper       15 ppm                                     Magnesium  22 ppm                                                             ______________________________________                                    

The distillation procedure described above produces two essentialbenefits to the process stream prior to solvent extraction; (i) thereduced ammonia concentration significantly enhances the solventextraction kinetics thereby reducing both the size of the solventextraction cells and their number; (ii) the effect of heat on theProduct Liquor stream causes coagulation and precipitation of importantimpurity elements such as iron, manganese, silica and arsenic togetherwith the removal of other impurities such as organic polymerflocculants.

The removal of the above impurities greatly enhances the efficiency ofthe solvent extraction process and eliminates the formation of "crud" inthe settling section of the solvent extraction cells. The absence of a"crud" phase allows the solvent extraction cells to be operatedcontinuously.

The removal of these impurity solids is effected by passing the specialproduct liquor stream (3) to a Thickener, vessel (C). The underflowslurry (4) from this vessel contains the impurity elements listed abovetogether with some nickel and this is returned to the plant stockpile toenable the nickel to be recovered.

The solvent extraction nickel cobalt separation efficiency dependslargely on the presence of cobalt III compounds and absence of cobalt IIcompounds in the special Product liquor stream (3). The presence ofcobalt II compounds in the special product liquor stream can be causedby factors such as insufficient aeration of the ore/liquor slurry duringleaching of the reduced ore in the Aeration and Leaching Banks (D) andor post leaching conversion of Co III compounds to Co II compounds byreducing substances in either the product liquor or special productliquor.

Irrespective of the mode of formation of cobalt II in special productliquor it is essential that the element be reoxidised to oxidation stateIII prior to solvent extraction.

The reoxidation of cobalt II to cobalt III is essential for two mainreasons: (i) cobalt II is extracted together with nickel II by theorganic reagent and subsequent stripping of the organic reagent withammonia-ammonium carbonate solution to recover nickel may also removethe cobalt II thereby contaminating the essentially pure nickel solutionand resulting in a loss of some cobalt; (ii) The cobalt II organicreagent complex can undergo oxidation within the solvent extractioncells in which case the cobalt cannot be stripped from the organicreagent by normal procedures. The accumulation of cobalt II and III onthe organic phase, as must occur over an extended period of operation,results eventually in the nickel extracting power of the reagent beingreduced.

The reagent has not been permanently lost as special techniques havebeen developed by the inventor to treat the reagent and remove thecobalt thus restoring the reagent to its full nickel loading capacity,but this entails additional costs.

In order to reduce the concentration of cobalt II compounds present inspecial product liquor to a minimum prior to solvent extraction thecooled special product liquor is passed through storage tanks (E, F) inwhich the liquor is continuously aerated by the injection of air throughsintered stainless steel tubes (5).

Provided the size of the tanks is correctly gauged to allow adequateretention time for the oxygen in the air to oxidise the cobalt IIcompounds to cobalt III compounds the exiting liquor will contain lessthan five parts per million cobalt Il.

It is desirable to reduce this cobalt II level even further since indoing so the volume of organic reagent that has to be specially treatedto strip the cobalt from the organic reagent is greatly reduced thussaving additional treatment costs.

It has been found that the addition of hydrogen peroxide to specialproduct liquor provides the additional oxidising power necessary tolower the cobalt II concentration to one part per million or less in thespecial product liquor. Hydrogen peroxide is added to the aeratedspecial product liquor prior to the liquor being pumped into adiatomaceous earth filter (G) to remove any fine suspended solids.

The effluent from the filter system (G) is now ready for the solventextraction separation of nickel and cobalt. The filtration procedurecompletes the solution preparation phase.

SOLVENT EXTRACTION

In this section of the Pilot Plant the object is to use an organicreagent mixture in hydrocarbon solvent to separate nickel and cobalt andrecover the nickel in an ammonium carbonate strip liquor therebyallowing the organic reagent mixture to be continually recycled forfurther nickel loading duties.

A number of organic reagent mixtures can be used giving satisfactoryresults, however this Pilot Plant description covers the use of amixture of 2-hydroxy-5-t-nonylacetophenone oxime, isotridecanol andaliphatic kerosene, the proportions being adjusted to yield optimumstripping and extraction properties.

The special product liquor stream (6) is pumped at the rate of 35liters/minute into the mixer box of extraction cell El where it contactsthe partially nickel loaded organic reagent exiting extraction cell E2and also flowing at a rate of 35 liters/minute. The mixed phasesoverflow the mixer box and separate in the settler section of thesolvent extraction Cell, the organic phase rising to the top of theaqueous, heavy phase underneath. The phases flow cocurrently in thecells but countercurrently between the cells. The process of mixing andseparation is repeated in each cell with the aqueous phase (7) exitingextraction cell E3 being essentially free of nickel while the organicphase (8) exiting extraction cell El being free of cobalt and loadedwith nickel.

As it is standard practice and is known to those skilled in the art ofsolvent extraction, provision has been made in the design of-theextraction cells to allow some of the aqueous phase in each cell to berecycled back to the mixer box. This is an important facility as itallows for the use of a ratio of organic/aqueous in excess of 1.0overall in the circuit while maintaining a ratio of 1.0 in the mixerboxes. The ratio of 1.0 organic to aqueous in the mixer is desirable asit facilitates the mixing and metal transfer properties of the phases.

METAL STRIPPING

It is well known to those experienced in the art of metal recovery fromores using ammonia-ammonium carbonate leach solutions that both ammoniaand carbon dioxide can be recovered from solutions thereof by steamdistillation. The resulting solutions of ammonia and carbon dioxideobtained by condensing the vapours from such distillation procedures mayrequire modification before being used as stripping reagents in thesolvent extraction process.

The composition of the ammonia-ammonium carbonate stripping solution isa vital factor in controlling the efficiency of the solvent extractionoverall process. The condensate (9) from the Gas Cooler Condensers (H)can be modified by the injection of anhydrous ammonia gas (10) or byinjection of carbon dioxide gas (11) to achieve the desired result.

The resulting strip liquor of suitable composition (12) is pumped atapproximately 4 liters per minute into the mixing box of strip cell S3where it contacts both the partially stripped organic reagent mixtureexiting strip cell S2 at 35 liters per minute and an amount of recycleaqueous phase from strip cell S3 equal to approximately 31 liters perminute. This combination of solution streams gives an organic to aqueousratio in the mixer box of cell S3 of approximately 1:1, which isdesirable for both mixing and metal transfer reasons.

As described above for the extraction cells the mixed phases overflowthe S3 mixer box and separate in the settler section of the cell. Thepartially nickel loaded strip liquor moves forward to the mixer box ofstrip cell S2 where it contacts the partially stripped organic reagentmixture exiting strip cell S1. The stripped organic reagent mixture (13)exiting strip cell S3, now referred to as stripped organic gravitates toan intermediate reagent storage tank from which it is pumped toextraction cell E3 to recommence separating nickel from the incomingspecial product liquor stream (6).

The strip liquor exiting strip cell S2 enters the mixer box of stripcell S1 where it contacts both the incoming nickel loaded organicreagent exiting extraction cell E1 and a metered flow of recycle aqueousphase from the settler section of strip cell S1 to enable an organic toaqueous ratio of approximately 1:1 to be achieved.

The aqueous phase exiting the strip cell S1 is referred to as the loadedstrip liquor (14) and may contain 80 gl⁻¹ nickel, 270 gl⁻¹ NH₃ and 230gl⁻¹ CO₂ together with some impurity elements such as copper, cobalt andmagnesium.

It will be noted by people with prior experience in solvent extractionand metal separation that the above description of the mixer settlers isgeneral in nature and that other equipment is available that willproduce essentially the same result. It is also important to controltime and temperature of mixing and the method of pumping and mixing inorder to maximise the rate and extent of metal transfer and minimise theextent of organic reagent loss by both entrainment and degradation.

It will also be known to those with prior knowledge of the art that thecontinuity of the phases can greatly influence phase separation andreagent losses by entrainment. The change from aqueous phase continuousto organic phase continuous can be readily implemented and evaluated.

It should be apparent to those skilled in the art that the efficienciesof both the extraction and the stripping process are intimatelyassociated with both the organic reagent mixture and the strip liquorcomposition considered on a molar ratio basis.

The total nickel loading capacity of the organic reagent mixture willgovern the organic to aqueous ratio flow rates. The nickel loadingcapacity must exceed the concentration of nickel in the special productliquor in order to remove all the nickel from this stream at an organicto aqueous flow ratio of 1:1. The composition of the organic reagentmixture must be controlled so that it will rapidly release the complexednickel to the strip liquor when so contacted. As a result of manystudies it has been found that a reagent mixture containing 27.5 to 35%V/V of 2-hydroxy-5-t-nonyl acetophenone oxime and 15.5 to 20% V/Viso-tridecanol modifier diluted to 100% with an aliphatic-aromatickerosene is a suitable reagent mixture for both extraction andstripping.

The composition of the strip liquor is also extremely important as itmust have suitable stripping power to remove nickel from the nickelorganic reagent complex to a sufficiently low residual nickel value suchthat the stripped organic reagent nickel loading Capacity is in excessof the nickel in the incoming special product liquor stream. As a resultof many studies it has been found that a suitable strip liquor will havean ammonia content of 250-280 grams per liter and a carbon dioxidecontent of 220-250 grams per liter.

Typical equilibrium data for both the extraction and stripping circuitsis presented in Table No. 15.

                  TABLE NO. 15                                                    ______________________________________                                        OPERATING CONDITIONS                                                          Reagent:  30% V/V 2-hydroxy-5-nonylacetophenone oxime                                   17% V/V isotridecylalcohol                                                    53% V/V S2046 Kerosene                                              Three extraction cells - three strip cells                                    Organic/Aqueous 1:1 on extract side                                           Organic/Aqueous 9:1 on strip side                                             Strip Liquor: NH.sub.3 266 gl.sup.-1, CO.sub.2 220 gl.sup.-1                  Special Product Liquor: Ni 7.3 gl.sup.-1, Co 0.35 gl.sup.-1                   EXTRACTION EQUILIBRIUM                                                                    CELL 2                                                            CELL 1      Or-               CELL 3                                          Organic                                                                              Aqueous  ganic   Aqueous Organic                                                                              Aqueous                                Ni   Co    Ni    Co   Ni  Co  Ni   Co   Ni   Co  Ni   Co                      ______________________________________                                        *12.0                                                                              12    2.9   350  6.8 8   0.21 350  4.32 8   0.024                                                                              352                     ______________________________________                                        STRIPPING EQUILIBRIUM                                                         CELL 1      CELL 2        CELL 3                                              Organic                                                                              Aqueous  Organic  Aqueous                                                                              Organic                                                                              Aqueous                                Ni   Co    Ni     Co  Ni   Co   Ni  Co  Ni   Co  Ni   Co                      ______________________________________                                        10.4 8     88.6   6   8.4  8   76.8 1   3.7  4   51.0 1                       ______________________________________                                         *Ni values reported as gl.sup.-1, cobalt values in ppm.                  

The composition of the aqueous phase exiting Cell 1 of the strippingcircuit illustrates the excellent ratio of nickel to cobalt achieved.From a Ni/Co of 20.9 in the Special Product Liquor the invention hasenabled this to be upgraded to a Ni/Co ratio in excess of 14,000. Anickel product containing 99% nickel produced from this liquor wouldcontain less than 0.007% cobalt as an impurity.

In the above example it will be noted that the emphasis has been placedon the composition of the loaded strip liquor stream (14) and theconcentration of nickel therein. A feature of the invention is that itallows the concentration of the Loaded strip liquor stream (14) and thecomposition of the Raffinate stream (7) to be optimized.

The following example will illustrate how the nickel content of theRaffinate stream (7) can be reduced while maintaining the purity of theloaded strip liquor stream (14).

                                      TABLE NO. 16                                __________________________________________________________________________    OPERATING CONDITIONS                                                          Reagent:  30% V/V 2-hydroxy-5-nonylacetophenone oxime                                   17% V/V isotridecylalcohol                                                    53% V/V S2046 Kerosene                                              Three extraction cells - three strip cells                                    Organic/Aqueous 1:1 on extract side                                           Organic/Aqueous 8:1 on strip side                                             Strip Liquor: NH.sub.3 285 gl.sup.-1, CO.sub.2 260 gl.sup.-1                  Special Product Liquor: Ni 9.0 gl.sup.-1, Co 0.38 gl.sup.-1                   EXTRACTION EQUILIBRIUM                                                        CELL 1     CELL 2       CELL 3                                                Organic                                                                            Aqueous                                                                             Organic                                                                             Aqueous                                                                              Organic                                                                             Aqueous                                         Ni Co                                                                              Ni                                                                              Co  Ni Co Ni Co  Ni Co Ni Co                                           __________________________________________________________________________    *9.2                                                                             24                                                                              2.5                                                                             350 3.36                                                                             16 0.141                                                                            350 0.88                                                                             16 0.012                                                                            352                                          __________________________________________________________________________    STRIPPING EQUILIBRIUM                                                         CELL 1       CELL 2      CELL 3                                               Organic                                                                              Aqueous                                                                             Organic                                                                             Aqueous                                                                             Organic                                                                             Aqueous                                        Ni  Co Ni  Co                                                                              Ni  Co                                                                              Ni  Co                                                                              Ni  Co                                                                               Ni Co                                         __________________________________________________________________________    7.2 24 74.2                                                                              2 3.28                                                                              16                                                                              48.0                                                                              1 0.72                                                                              16                                                                              17.4                                                                              1                                          __________________________________________________________________________     *Ni values reported as gl.sup.-1, cobalt values in ppm.                  

The results show that a nickel content in Raffinate of 12 ppm wasachieved concurrently with a loaded strip liquor concentration of 74gl⁻¹ nickel. It must also be evident that this nickel level in Raffinatecould be lowered further if operating conditions allowed economicaltreatment of a loaded strip nickel of less than 74 gl⁻¹ nickel.

As will be immediately evident to those with prior knowledge of the artthe above examples of solution composition represent but two of a numberof possible combinations which will suit a particular situation and aregiven without the intention that the examples are the only onespossible.

The loaded strip liquor (14) exiting strip cell S1 can now be treated ifrequired to enhance the ratio of nickel to impurity elements.

LOADED STRIP LIQUOR PURIFICATION

The impurity elements such as manganese and iron are reduced to levelsof the order or one part per million or less in the special productliquor by means of the ammonia distillation procedure described above.Metals such as copper that form stable ammines in ammonium carbonatesolution will remain in solution during the distillation procedure andwill, if present as cupric ions, extract into the organic reagent in asimilar manner to nickel II and cobalt II.

It may be depending on the composition of the organic reagent mixture,that the copper distributes its concentration between the strip liquorand the organic reagent in a favourable fashion during stripping so thatthe nickel to copper ratio in the loaded strip liquor is satisfactoryfor specification purposes. On the other hand the copper may be strippedby the ammonia-ammonium carbonate strip liquor from its organic complexwith similar facility to nickel and if present initially in the specialproduct liquor at an unfavourable nickel to copper ratio the copper willhave to be removed from the loaded strip liquor before a satisfactorynickel product can be produced.

Ammonium hydrosulphide is an effective sulphiding agent, particularly inammoniacal solutions and there are many examples where it is used toprecipitate metals from solution as insoluble sulphides. It is not aspecific precipitating reagent but can nevertheless be used to sulphideone metal more favourably than another.

Injection of ammonium hydrosulphide (15) into a highly turbulent streamof loaded strip liquor (14) will result in the instant precipitation ofa mixed sulphide of copper and nickel. If the ratio of nickel to copperin the loaded strip liquor is, for example, 700:1 then a mixed coppernickel sulphide of nickel to copper ratio of 0.5:1 can be recovered.Those with a knowledge of solubility product chemistry will appreciatewhy this is possible. No excess sulphur anions are introduced into theloaded strip liquor since all the sulpur anions will be removed with theprecipitated mixed nickel copper sulphides.

The precipitated sulphides can be readily removed from solution byflocculation with organic polymers followed by filtration through aconventional industrial filter, such as copper sulphide filter 15(a) toproduce a purified loaded strip liquor (16).

STEAM STRIPPING

It is the purpose of this process to remove ammonia and carbon dioxidefrom the purified loaded strip liquor stream thereby destabilising theammine complex of nickel resulting in precipitation of the nickel as abasic nickel carbonate of high purity. The purified loaded strip liquorstream (16) is pumped into a multiple plate distillation column (1) intothe base of which is injected low pressure steam (2). The amount ofsteam necessary to effect complete precipitation of the nickel as basicnickel carbonate will vary with the nature of the purified loaded stripliquor stream, however a value of 0.6 kg steam per liter of feed liquorhas been determined in trails.

The vapours from the distillation column (17) consisting essentially ofwater, ammonia and carbon dioxide are condensed in a Gas CoolerCondenser (H) and the condensate after concentration adjustment by theaddition of either ammonia gas (10) or carbon dioxide gas (11) is termedstrip liquor (12) and is recycled to strip cell S3 in the solventextraction area.

The product stream from the distillation column consisting of a mixtureof basic nickel carbonate and water of approximately 25% W/V solids istermed product magma (18) and is pumped to a Thickener (J) to increasethe solids content of the slurry to approximately 50% W/V before furtherprocessing. Those familiar with handling suspensions of solids inaqueous streams will understand that organic flocculants may be added tothe dilute slurry stream (18) to promote the production of a denseThickener underflow product while at the same time producing an overflowstream almost free of suspended solids.

The clean aqueous overflow stream (19) may contain traces of ammonia ofthe order of 100 parts per million, soluble nickel of the order of 3parts per million together with suspended basic nickel carbonate solids,that have not been collected by the flocculation process, of the orderof 5 parts per million. This stream could be recycled directly to theplant as a source of good quality water, however as its temperature isabove 50° C. it is first diverted to a cooling pond. The cooling pondserves a dual purpose in that while the aqueous phase is cooling below50° C. it also allows any valuable suspended basic nickel carbonatesolids to settle out for later recovery and recycle to the processingplant.

NICKEL RECOVERY

The nickel may be recovered as a basic nickel carbonate from stream (24)by any conventional manner.

The basic nickel carbonate solids produced are very pure, free of theanions of sulphur and have the general formula NiCO₃.4Ni(OH)₂. There area number of ways in which the basic nickel carbonate may be processed toproduce nickel products. Those experienced in metal productiontechniques will be aware that the basic nickel carbonate can beredissolved in ammonia-ammonium salt liquors and then subjected to highpressure hydrogen reduction to produce nickel metal of high purity.Alternatively the basic nickel carbonate can be calcined to produce bothblack and green nickel oxides which are also saleable products. Thenickel oxides can be converted to nickel metal by reduction withhydrogen at moderate temperatures.

Basic nickel carbonate solids recovered from process streams containingsulphur anions at the time of distillation precipitation are alwayscontaminated with sulphur compounds. The solids obtained from such adistillation precipitation are in fact a mixture of basic nickelcarbonate and basic nickel sulphate. Processing these solids via thecalcination-reduction route to produce a low sulphur nickel productrequires temperatures in the oxidative calcination stage of the order of1200° C.

A significant benefit of the present invention is that it eliminatessulphur anions prior to the distillation-precipitation recovery of basicnickel carbonate solids. Basic nickel carbonate solids recovered free ofcontaminating sulphur compounds can be converted to nickel oxide powderat temperatures in the range of 450-550° C. A substantial savings inenergy accrues by processing at lower temperature.

This low temperature calcination facilitates the hydrogen reduction stepwhich proceeds more rapidly with nickel oxide produced at a lowtemperature, consequently more energy savings are made or the sameenergy inputs will result in significantly higher productivity.

Commencing with basic nickel carbonate the route to nickel metal mayproceed by initially heating the basic nickel carbonate in a Calciner ata suitably low temperature to produce black nickel oxide followed byreduction of the black nickel oxide in a heated hydrogen furnace toproduce nickel metal.

Alternatively the conversion of the basic nickel carbonate to nickeloxide followed by reduction of the oxide metal may be achieved in oneoperation by careful control of the atmosphere and temperature of thereaction vessel. The offgas from the reaction vessel should have acarbon monoxide (CO) content of approximately 1.5% to achieve therequired in-furnace reduction efficiency. The choice of fuel to produceboth the heat and reducing atmosphere necessary is very important. Theknown ability of nickel oxide to react quickly with oxides of sulphurprecludes the use of fuels containing sulphur if a low sulphur nickelmetal is the desired end result.

A third Process is to commit the basic nickel carbonate directly to anelectrically heated furnace through which a stream of hydrogen gas ispassed. The decomposition of the basic nickel carbonate to nickel oxideis followed by reduction of the nickel oxide to nickel metal without anycontamination of the metal by sulphur.

An example of such a product produced by the above process of heating inhydrogen gas is as follows:

                  TABLE 16                                                        ______________________________________                                        Ni   Co     Fe     Mn   Mg   C    S    As   Zn   Cu                           ______________________________________                                        99.30                                                                              0.04   0.13   0.02 0.12 0.02 0.005                                                                              0.0001                                                                             0.02 0.05                         ______________________________________                                    

COBALT RECOVERY

The aqueous stream exiting the E3 extraction cell is called theRaffinate (7) and contains a mixture of cobalt ammines with cobalt inoxidation state (III).

Efficient operation of the solvent extraction process will control thelevel of nickel impurity in the raffinate and this has been found in thePilot Plant to average 20 parts per million. With a cobalt concentrationof, on average, 400 parts per million in the raffinate stream the nickelrepresents a significant impurity. The raffinate stream may also containother impurities although these would be of a minor nature compared withnickel.

The present invention utilizes the efficiency of the hydrosulphide ionin precipitating insoluble metal sulphides from dilute solution. Thisprocedure separates nickel and cobalt from elements such as magnesiumthat do not under these conditions form insoluble sulphides, releasesthe solution which contains approximately 25 grams per liter ammonia and15 grams per liter carbon dioxide for recycling back to the process andserves to isolate the metals in a concentrated form.

The raffinate stream (7) is injected with ammonium hydrosulphide (15) ata ratio of approximately one part ammonium hydrosulphide liquor to 170parts of raffinate. The reaction is carried out in a tube reactor inwhich the solutions are in a turbulent state. It is desirable to addsufficient ammonium hydrosulphide liquor to remove all of the cobaltfrom solution and at the same time allowing as much nickel as possibleto remain in solution. Realization of this aim will result in extremelylow levels of excess hydrosulphide ion in the sulphided raffinate.

The addition of organic flocculating agents to the sulphided liquorenables the sulphide solids to be concentrated in a Thickener (K) beforethe underflow of solids is dehydrated in a Spray Dryer (L) prior tofurther treatment or sale as a cobalt nickel sulphide product.

The clean liquid overflow from Thickener (K) will now be almost free ofmetals and have an ammonia and carbon dioxide content similar to theincoming Special Product Liquor stream. This liquor (20) is of asuitable composition to be returned to the ore leaching-washing circuitThickener No. 7aorganic reagent selected from the group consisting of2-hydroxy-5-t-nonyl acetophenoneoxime, 2-hydroxy-5-nonylsalicylaldoxime, alkyl, aryl and halide substituted beta diketones.

We claim:
 1. A Process for the separation and recovery of nickel from anammoniacal ammonium carbonate liquor containing nickel II ions andcobalt III ions by liquid-liquid extraction including the successivesteps of:(a) oxidising the majority of any cobalt II ammines in theammoniacal liquor to cobalt III; (b) extracting nickel from theammoniacal liquor with an organic reagent organic reagent selected fromthe group consisting of 2-hydroxy-5t-nonyl acetophenoneoxime,2-hydroxy-5-nonyl salicylaldoxime, alkyl, aryl and halide substitutedbeta diketones to form a nickel loaded organic phase and an ammoniacalammonium carbonate phase containing cobalt; and (c) stripping the nickelloaded organic phase; characterised in that the nickel loaded organicphase is stripped by contacting the organic phase with an ammoniacalammonium carbonate solution to form a nickel loaded aqueous strip liquorand in that ammoniacal ammonium carbonate solutions are the only aqueousphases involved in the process.
 2. A process as claimed in claim 1,characterised in that the ammoniacal ammonium carbonate liquorcontaining the nickel and cobalt is heated prior to step (a) so as toprecipitate impurities and reduce the ammonium content.
 3. A process asclaimed in claim 2, characterised in that the ammoniacal ammoniumcarbonate liquor is heated to a temperature of about 100° C. atatmospheric pressure and the ammonium content reduced to between 22 to32 gl⁻¹
 4. A process as claimed in claim 3, characterised in that theammoniacal ammonium carbonate liquor comprises ammonia and carbondioxide the ammonia content is reduced to 25 gl⁻¹ and the carbon dioxidecontent is 18 gl⁻¹.
 5. A process as claimed in claim 1, characterised inthat the cobalt II ammines are oxidised to cobalt III by oxidising withair or air in combination with hydrogen peroxide.
 6. A process asclaimed in claim 5, characterised in that the ammoniacal liquor containsless than 1 ppm cobalt II after oxidation, at 50° C. and atmosphericpressure.
 7. A process as claimed in claim 1 characterised in that theliquid organic solution also- contains a modifying reagent selected fromthe group consisting of an alcohol, an aliphatic or aromatic kerosenecarrier and a combination of an alcohol with an aliphatic or aromatickerosene carrier.
 8. A process as claimed in claim 7, characterised inthat the modifying reagent is an alcohol selected fromiso-tridecylalcohol, iso-undecylalcohol, iso-dodecylalcohol and thecorresponding linear types.
 9. A process as claimed in claim 8,characterised in that the alcohol is iso-tridecylalcohol.
 10. A processas claimed in claim 7, characterised in that the organic solutioncomprises 32.5% v/v 2-hydroxy-5-nonylaceto-phenoneoxime, 18.4% v/viso-tridecylalcohol with 49.1% v/v hydrocarbon solvent of less than 25%aromatic content.
 11. A process as claimed in claim 1, characterised inthat the ammoniacal liquor is contacted with the liquid organic solutioncontaining the organic reagent for a period of between 30 seconds and 60minutes.
 12. A process as claimed in claim 11, characterised in that theammoniacal liquor is contacted with the liquid organic solutioncontaining the organic reagent for a period of 3 minutes.
 13. A processas claimed in claim 1, characterised in that the nickel loaded organicphase is stripped by contact with the ammoniacal ammonium carbonatesolution for a period sufficient to allow the nickel to pass from theorganic phase to an aqueous strip liquor phase
 14. A process as claimedin claim 13, characterised in that the contact period is from 30 secondsto 60 minutes.
 15. A process as claimed in claim 14, characterised inthat the ammoniacal ammonium carbonate strip liquor is contacted withthe nickel loaded organic phase for a period of 3 minutes.
 16. A processas claimed in claim 1, characterised in that the nickel loaded organicphase is stripped in a stripping cell at a temperature of about 40° C.17. A process as claimed in claim 13, characterised in that theammoniacal ammonium carbonate solution contains a total ammoniaconcentration of from 210 to 300 gl⁻¹ and a total carbon dioxideconcentration of from 150 to 300 gl⁻¹.
 18. A process as claimed in claim17, characterised in that the nickel loaded aqueous strip liquor phasecontains an ammonia concentration of about 285 gl⁻¹ and a carbon dioxideconcentration of about 230 gl⁻¹.
 19. A process as claimed in claim 1,characterised in that the nickel loaded organic phase is separated fromthe ammoniacal ammonium carbonate phase containing the cobalt and thenickel stripping process is carried out by means of a conventional batchextraction or continuous mixer settler techniques.
 20. A process asclaimed in claim 1, characterised in that three extraction and threestrip stages are carried out with recycling of the aqueous solution tomaintain an aqueous to organic ratio of 1:1 in the mixer boxes.
 21. Aprocess as claimed in claim 1, characterised in that the nickel isrecovered from the nickel loaded aqueous strip liquor phase as basicnickel carbonate by means of distillation of the liquor.
 22. A processas claimed in claim 1, characterised in that the cobalt is recoveredfrom the ammoniacal ammonium carbonate phase by means of steam heating,sulphide addition or ion exchange procedures.